The present invention relates generally to a detector assembly, and, more particularly to a two piece collimator assembly with improved design flexibility.
Computed tomography has been utilized for a wide variety of imaging applications. One such category of applications is comprised of medical imaging. Although it is known that computed tomography may take on a wide variety of configurations within the medical industry, it commonly is based on the transmission of low energy rays through a body structure. These low energy rays are subsequently received and processed to formulate an image, often three-dimensional, of the body structure that can by analyzed by clinicians as a diagnostic aid.
The reception of the low energy rays, such as gamma rays or x-rays, is often accomplished through the use of a device referred to as a detector assembly. The detector assembly is typically comprised of a plurality of structures working in concert to receive and process the incoming energy rays after they have passed through the body structure. The detector assembly utilizes scintillator to absorb the photons and convert their energy into visible light. This allows the low energy rays received by the scintillator detector to be converted into useful information. Scintillator elements may come in a wide variety of forms and may be adapted to receive a wide variety of incoming rays. The light produced by the scintillator element is commonly processed by way of a device such as a light sensitive photodiode, which converts the light from the scintillator element into an electronic signal. In this fashion, the information from the scintillator detector can be easily transferred, converted, and processed by electronic modules to facilitate viewing and manipulation by clinicians.
Imaging assemblies additionally include an element referred to as a collimator. A collimator is an element that commonly incorporates two fundamental functions. The collimator is used to reduce x-ray scatter as the x-rays approach the scintillator element. Scattered photons can cause noise and reduce resolution causing image artifacts. In addition, the collimator is commonly used as a shielding device for shielding the edges of the individual scintillator cells. This is necessary to prevent, X-rays from impinging on the edges of the scintillators causing non linearities and image artifacts, x-rays from damaging the reflector between scintillator elements, X-rays being transmitted through the gap between scintillator elements and impinging on the photo diode causing noise or X-rays being transmitted through the gap between scintillator elements and impinging on electronics located behind the detector causing damage to these sensitive electronic components. Thus present collimator designs commonly attempt to balance shielding and scatter reducing properties.
Unfortunately, the design characteristics that make a collimator optimal for shielding the scintillator edges are not always compatible with the characteristics that make a collimator optimal for reducing x-ray scatter. Present collimator formation, therefore, often relies on a functional compromise between these two competing characteristics. Even when the physical characteristics necessary to perform each of these functions is not directly incompatible, their importance may vary by function. High manufacturing and assembly tolerances are often important for proper shielding functionality. These high tolerances, however, are not commonly required to reduce x-ray scatter. Therefore, by requiring the collimator assembly to be manufactured with tolerances suitable for shielding, the cost of the entire assembly is often increased.
Approaches to resolving this balance of characteristics has lead some to modify other aspects of the detector assembly to accommodate existing collimator designs. These approaches include leaving large gaps between adjoining scintillator elements; use of x-ray absorbing layers between scintillator cells; and the use of organic reflector composites. In these approaches, however, the distance between scintillator elements tends to be large. This is often incompatible with the small cell and small gap requirements for the current generation of multi-slice CT systems. In addition, many existing systems do a poor job of attenuating scatter x-rays within the scintillator elements or to prevent X-rays from crossing over from one scintillator cell to an adjoining cell. Thus considerable room for improvement of existing designs and design approaches exists.
It would, however, be highly desirable to have a detector assembly that could be simultaneously optimized for reducing scattering x-rays in addition to shielding scintillator elements. Similarly, it would be highly desirable to have a detector assembly suitable for use in modern high density imaging applications.